When to use earlier/before?

Question

Is there a correct usage - when to use the word earlier and when to use the word before?

I always thought that a past tense sentence referring to something that happened previously should use earlier. But recently I've seen before used in otherwise well edited books.

Ex. She thought back to the fight she'd had earlier that day.

He was reminded of the party he'd been at three years before.

Is one way more correct than the other?

Please include source.

Answer 1

Earlier is an a adverb if it modifies the verb, e.g. "I should get out of bed earlier.", or an adjective if it modifies a noun referring to a period of time or any event, e.g. "I should get up at an earlier hour." or "The topic was discussed at an earlier meeting."

Before is a preposition, e.g. "I should get up before noon if I ever want to get anything done."